Medium-sized cyclophanes. Part XVI. Substitution versus transannular reaction of [2.2]metacyclophanes with benzoyl peroxide and cupric chloride. Importance of a cation radical intermediate in the transannular dehydrogenation

1974 ◽  
pp. 577 ◽  
Author(s):  
Kozaburo Nishiyama ◽  
Kazuo Hata ◽  
Takeo Sato
Keyword(s):  
Benzoyl Peroxide ◽  
Cation Radical ◽  
Cupric Chloride ◽  
Radical Intermediate ◽  
Transannular Reaction

Observation of a radical intermediate in the one electron oxidation of 5-methyl-1-thia-5-azacyclooctane by •Br2−

1984 ◽  
Vol 62 (9) ◽  
pp. 1874-1876 ◽  
Author(s):  
Warren Kenneth Musker ◽  
Parminder S. Surdhar ◽  
Rizwan Ahmad ◽  
David A. Armstrong
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Half Life ◽  
Cation Radical ◽  
Order Rate Constant ◽  
Type Structure ◽  
Radical Intermediate ◽  
Text Type ◽  
First Order ◽  
The One

The one electron oxidant •Br2− reacts with 5-methyl-1-thia-5-azacyclooctane (4) in aqueous solution at high pH with an overall rate constant of ~2 × 108 M s−1. The radical intermediate produced has a broad maximum at 500 nm with ε = 2400 M−1 cm−1 and at pH 10 decays with a first order rate constant of 2.3 ± 0.3 × 104 s−1, first half-life of 30 ± 5 μs. Its characteristics do not correspond to those of the [Formula: see text] species reported by Asmus and co-workers. The species appears to be the same as the cation radical reported earlier in the one electron oxidation of 4 in acetonitrile. This species is considered to have an [Formula: see text] type structure, which provides transannular stabilization.

ChemInform Abstract: Hypervalent Iodine Induced Oxidative Cross Coupling via Thiophene Cation Radical Intermediate.

ChemInform ◽  
2013 ◽  
Vol 44 (18) ◽  
pp. no-no
Author(s):  
Toshifumi Dohi ◽  
Motoki Ito ◽  
Sho Sekiguchi ◽  
Yohei Ishikado ◽  
Yasuyuki Kita
Keyword(s):  
Cation Radical ◽  
Cross Coupling ◽  
Hypervalent Iodine ◽  
Radical Intermediate

Light-induced Free Radical Oxidation of 2-Oxo-1,2,3,4-tetrahydropyrimidines

2012 ◽  
Vol 67 (3) ◽  
pp. 263-268
Author(s):  
Hamid Reza Memarian ◽  
Leila Hejazi ◽  
Asadallah Farhadi
Keyword(s):  
Benzoyl Peroxide ◽  
Free Radical Oxidation ◽  
Phenyl Group ◽  
Heterocyclic Ring ◽  
Radical Intermediate ◽  
Radical Oxidation ◽  
Photo Oxidation ◽  
Rate Determining Step ◽  
The Stability ◽  
Allylic Radical

A variety of 4-substituted 5-acetyl- and 5-carboethoxy-2-oxo-1,2,3,4-tetrahydropyrimidines were oxidized under UV irradiation in the presence or absence of benzoyl peroxide. The nature of the substituents on the 4- and 5-positions of the heterocyclic ring affects the rate of photo-oxidation, and irradiation of these compounds in the presence of benzoyl peroxide decreases the time of reaction drastically. Removal of 4-H by a benzoyloxy radical under formation of a trihydropyrimidinoyl radical intermediate occurs in the rate-determining step. The stability of this benzylic and allylic radical intermediate is affected by the nature and the position of the additional substituent on the phenyl group located at C-4.

scholarly journals Ligninase of Phanerochaete chrysosporium. Mechanism of its degradation of the non-phenolic arylglycerol β-aryl ether substructure of lignin

1986 ◽  
Vol 236 (1) ◽  
pp. 279-287 ◽  
Author(s):  
T K Kirk ◽  
M Tien ◽  
P J Kersten ◽  
M D Mozuch ◽  
B Kalyanaraman
Keyword(s):  
Aromatic Ring ◽  
Cation Radical ◽  
Aryl Ether ◽  
Model Compounds ◽  
Radical Intermediate ◽  
Cation Radicals ◽  
Basic Model ◽  
Lignin Model ◽  
Time Courses ◽  
Dimeric Model

This study examined the ligninase-catalysed degradation of lignin model compounds representing the arylglycerol beta-aryl ether substructure, which is the dominant one in the lignin polymer. Three dimeric model compounds were used, all methoxylated in the 3- and 4-positions of the arylglycerol ring (ring A) and having various substituents in the beta-ether-linked aromatic ring (ring B), so that competing reactions involving both rings could be compared. Studies of the products formed and the time courses of their formation showed that these model compounds are oxidized by ligninase (+ H2O2 + O2) in both ring A and ring B. The major consequence with all three model compounds is oxidation of ring A, leading primarily to cleavage between C(alpha) and C(beta) (C(alpha) being proximal to ring A), and to a lesser extent to the oxidation of the C(alpha)-hydroxy group to a carbonyl group. Such C(alpha)-oxidation deactivates ring A, leaving only ring B for attack. Studies with C(alpha)-carbonyl model compounds corresponding to the three basic model compounds revealed that oxidation of ring B leads in part to dealkoxylations (i.e. to cleavage of the glycerol beta-aryl ether bond and to demethoxylations), but that these are minor reactions in the model compounds most closely related to lignin. Evidence is also given that another consequence of oxidation of ring B in the C(alpha)-carbonyl model compounds is formation of unstable cyclohexadienone ketals, which can decompose with elimination of the beta-ether-linked aromatic ring. The mechanisms proposed for the observed reactions involve initial formation of aryl cation radicals in either ring A or ring B. The cation radical intermediate from one of the C(alpha)-carbonyl model compounds was identified by e.s.r. spectroscopy. The mechanisms are based on earlier studies showing that ligninase acts by oxidizing appropriately substituted aromatic nuclei to aryl cation radicals [Kersten, Tien, Kalyanaraman & Kirk (1985) J. Biol. Chem. 260, 2609-2612; Hammel, Tien, Kalyanaraman & Kirk (1985) J. Biol. Chem. 260, 8348-8353].

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